/*
 *
 * checkpointer.cpp
 *
 * The checkpointer is new as of Postgres 9.2.	It handles all checkpoints.
 * Checkpoints are automatically dispatched after a certain amount of time has
 * elapsed since the last one, and it can be signaled to perform requested
 * checkpoints as well.  (The GUC parameter that mandates a checkpoint every
 * so many WAL segments is implemented by having backends signal when they
 * fill WAL segments; the checkpointer itself doesn't watch for the
 * condition.)
 *
 * The checkpointer is started by the postmaster as soon as the startup
 * subprocess finishes, or as soon as recovery begins if we are doing archive
 * recovery.  It remains alive until the postmaster commands it to terminate.
 * Normal termination is by SIGUSR2, which instructs the checkpointer to
 * execute a shutdown checkpoint and then exit(0).	(All backends must be
 * stopped before SIGUSR2 is issued!)  Emergency termination is by SIGQUIT;
 * like any backend, the checkpointer will simply abort and exit on SIGQUIT.
 *
 * If the checkpointer exits unexpectedly, the postmaster treats that the same
 * as a backend crash: shared memory may be corrupted, so remaining backends
 * should be killed by SIGQUIT and then a recovery cycle started.  (Even if
 * shared memory isn't corrupted, we have lost information about which
 * files need to be fsync'd for the next checkpoint, and so a system
 * restart needs to be forced.)
 *
 * Portions Copyright (c) 2020 Huawei Technologies Co.,Ltd.
 * Portions Copyright (c) 1996-2012, PostgreSQL Global Development Group
 *
 * IDENTIFICATION
 *	  src/gausskernel/process/postmaster/checkpointer.cpp
 *
 * -------------------------------------------------------------------------
 */
#include "postgres.h"
#include "knl/knl_variable.h"

#include <signal.h>
#include <sys/time.h>

#include "access/xlog_internal.h"
#include "access/xlog.h"
#include "libpq/pqsignal.h"
#include "miscadmin.h"
#include "pgstat.h"
#include "postmaster/bgwriter.h"
#include "postmaster/pagewriter.h"
#include "replication/syncrep.h"
#include "replication/ss_disaster_cluster.h"
#include "storage/buf/bufmgr.h"
#include "storage/ipc.h"
#include "storage/lock/lwlock.h"
#include "storage/smgr/knl_usync.h"
#include "storage/smgr/relfilenode_hash.h"
#include "storage/proc.h"
#include "storage/shmem.h"
#include "storage/smgr/smgr.h"
#include "storage/spin.h"
#include "utils/guc.h"
#include "utils/memutils.h"
#include "utils/resowner.h"
#include "gssignal/gs_signal.h"
#include "postmaster/pagewriter.h"

/* ----------
 * Shared memory area for communication between checkpointer and backends
 *
 * The ckpt counters allow backends to watch for completion of a checkpoint
 * request they send.  Here's how it works:
 *	* At start of a checkpoint, checkpointer reads (and clears) the request
 *	  flags and increments ckpt_started, while holding ckpt_lck.
 *	* On completion of a checkpoint, checkpointer sets ckpt_done to
 *	  equal ckpt_started.
 *	* On failure of a checkpoint, checkpointer increments ckpt_failed
 *	  and sets ckpt_done to equal ckpt_started.
 *
 * The algorithm for backends is:
 *	1. Record current values of ckpt_failed and ckpt_started, and
 *	   set request flags, while holding ckpt_lck.
 *	2. Send signal to request checkpoint.
 *	3. Sleep until ckpt_started changes.  Now you know a checkpoint has
 *	   begun since you started this algorithm (although *not* that it was
 *	   specifically initiated by your signal), and that it is using your flags.
 *	4. Record new value of ckpt_started.
 *	5. Sleep until ckpt_done >= saved value of ckpt_started.  (Use modulo
 *	   arithmetic here in case counters wrap around.)  Now you know a
 *	   checkpoint has started and completed, but not whether it was
 *	   successful.
 *	6. If ckpt_failed is different from the originally saved value,
 *	   assume request failed; otherwise it was definitely successful.
 *
 * ckpt_flags holds the OR of the checkpoint request flags sent by all
 * requesting backends since the last checkpoint start.  The flags are
 * chosen so that OR'ing is the correct way to combine multiple requests.
 *
 * num_backend_writes is used to count the number of buffer writes performed
 * by user backend processes.  This counter should be wide enough that it
 * can't overflow during a single processing cycle.  num_backend_fsync
 * counts the subset of those writes that also had to do their own fsync,
 * because the checkpointer failed to absorb their request.
 *
 * The requests array holds fsync requests sent by backends and not yet
 * absorbed by the checkpointer.
 *
 * Unlike the checkpoint fields, num_backend_writes, num_backend_fsync, and
 * the requests fields are protected by CheckpointerCommLock.
 *
 * fsync_request_launched, fsync_request_absorbed and fsync_request_finished are
 * used for communication between main pagewriter and checkpointer as following:
 * 1. main pagewriter sets fsync_request_launched to be true when it finds dw file is out of space.
 * 2. main pagewriter waits in a loop for fsync_request_finished to be set
 * 3. Before ckpt performs a smgrsync, it sets fsync_request_absorbed to be true and resets fsync_request_launched.
 * 4. After ckpt successfully finishes a smgrsync, it sets fsync_request_finished and resets fsync_request_absorbed.
 * 5. main pagewriter quits the above loop and resets fsync_request_finished.
 * Note: if multiple pagewriters are to be allowed to reset dw file, then each of them needs such three flags.
 * In the future, we may change dw file into a ring. Pagewriter will only wait for vaccant dw file space while dw file
 * is truncated solely by checkpointer through its smgrsync.
 * ----------
 */

typedef struct CheckpointerShmemStruct {
    ThreadId checkpointer_pid; /* PID (0 if not started) */
    slock_t ckpt_lck;          /* protects all the ckpt_* fields */
    int64 fsync_start;
    int64 fsync_done;
    int64 fsync_request;

    int ckpt_started; /* advances when checkpoint starts */
    int ckpt_done;    /* advances when checkpoint done */
    int ckpt_failed;  /* advances when checkpoint fails */

    int ckpt_flags; /* checkpoint flags, as defined in xlog.h */

    uint32 num_backend_writes; /* counts user backend buffer writes */
    uint32 num_backend_fsync;  /* counts user backend fsync calls */

    int num_requests;                /* current # of requests */
    int max_requests;                /* allocated array size */
    CheckpointerRequest requests[1]; /* VARIABLE LENGTH ARRAY */
} CheckpointerShmemStruct;

#ifdef ENABLE_MOT
typedef struct CheckpointCallbackItem {
    struct CheckpointCallbackItem* next;
    CheckpointCallback callback;
    void* arg;
} CheckpointCallbackItem;
#endif

extern volatile PMState pmState;

/* interval for calling AbsorbFsyncRequests in CheckpointWriteDelay */
#define WRITES_PER_ABSORB 1000

/* Prototypes for private functions */
static void CheckArchiveTimeout(void);
static bool IsCheckpointOnSchedule(double progress);
static bool ImmediateCheckpointRequested(void);
static bool CompactCheckpointerRequestQueue(void);
static void UpdateSharedMemoryConfig(void);

/* Signal handlers */
static void chkpt_quickdie(SIGNAL_ARGS);
static void ChkptSigHupHandler(SIGNAL_ARGS);
static void ReqCheckpointHandler(SIGNAL_ARGS);
static void chkpt_sigusr1_handler(SIGNAL_ARGS);
static void ReqShutdownHandler(SIGNAL_ARGS);

/*
 * Main entry point for checkpointer process
 *
 * This is invoked from AuxiliaryProcessMain, which has already created the
 * basic execution environment, but not enabled signals yet.
 */
void CheckpointerMain(void)
{
    sigjmp_buf local_sigjmp_buf;
    MemoryContext checkpointer_context;
    bool bgwriter_first_startup = true;

    t_thrd.checkpoint_cxt.CheckpointerShmem->checkpointer_pid = t_thrd.proc_cxt.MyProcPid;

    u_sess->attr.attr_storage.CheckPointTimeout = ENABLE_INCRE_CKPT
                                                      ? u_sess->attr.attr_storage.incrCheckPointTimeout
                                                      : u_sess->attr.attr_storage.fullCheckPointTimeout;
    ereport(
        LOG, (errmsg("checkpointer started, CheckPointTimeout is %d", u_sess->attr.attr_storage.CheckPointTimeout)));

    /*
     * Properly accept or ignore signals the postmaster might send us
     *
     * Note: we deliberately ignore SIGTERM, because during a standard Unix
     * system shutdown cycle, init will SIGTERM all processes at once.	We
     * want to wait for the backends to exit, whereupon the postmaster will
     * tell us it's okay to shut down (via SIGUSR2).
     */
    (void)gspqsignal(SIGURG, print_stack);
    (void)gspqsignal(SIGHUP, ChkptSigHupHandler);   /* set flag to read config
                                                     * file */
    (void)gspqsignal(SIGINT, ReqCheckpointHandler); /* request checkpoint */
    (void)gspqsignal(SIGTERM, SIG_IGN);             /* ignore SIGTERM */
    (void)gspqsignal(SIGQUIT, chkpt_quickdie);      /* hard crash time */
    (void)gspqsignal(SIGALRM, SIG_IGN);
    (void)gspqsignal(SIGPIPE, SIG_IGN);
    (void)gspqsignal(SIGUSR1, chkpt_sigusr1_handler);
    (void)gspqsignal(SIGUSR2, ReqShutdownHandler); /* request shutdown */

    /*
     * Reset some signals that are accepted by postmaster but not here
     */
    (void)gspqsignal(SIGCHLD, SIG_DFL);
    (void)gspqsignal(SIGTTIN, SIG_DFL);
    (void)gspqsignal(SIGTTOU, SIG_DFL);
    (void)gspqsignal(SIGCONT, SIG_DFL);
    (void)gspqsignal(SIGWINCH, SIG_DFL);

    /* We allow SIGQUIT (quickdie) at all times */
    sigdelset(&t_thrd.libpq_cxt.BlockSig, SIGQUIT);

    /*
     * Initialize so that first time-driven event happens at the correct time.
     */
    t_thrd.checkpoint_cxt.last_checkpoint_time = t_thrd.checkpoint_cxt.last_truncate_log_time =
        t_thrd.checkpoint_cxt.last_xlog_switch_time = (pg_time_t)time(NULL);

    /*
     * Create a resource owner to keep track of our resources (currently only
     * buffer pins).
     */
    t_thrd.utils_cxt.CurrentResourceOwner = ResourceOwnerCreate(NULL, "Checkpointer",
        THREAD_GET_MEM_CXT_GROUP(MEMORY_CONTEXT_STORAGE));

    /*
     * Create a memory context that we will do all our work in.  We do this so
     * that we can reset the context during error recovery and thereby avoid
     * possible memory leaks.  Formerly this code just ran in
     * t_thrd.top_mem_cxt, but resetting that would be a really bad idea.
     */
    checkpointer_context = AllocSetContextCreate(t_thrd.top_mem_cxt,
        "Checkpointer",
        ALLOCSET_DEFAULT_MINSIZE,
        ALLOCSET_DEFAULT_INITSIZE,
        ALLOCSET_DEFAULT_MAXSIZE);
    MemoryContextSwitchTo(checkpointer_context);

    /*
     * If an exception is encountered, processing resumes here.
     *
     * See notes in postgres.c about the design of this coding.
     */
    int curTryCounter;
    int* oldTryCounter = NULL;
    if (sigsetjmp(local_sigjmp_buf, 1) != 0) {
        gstrace_tryblock_exit(true, oldTryCounter);
        /*
         * Close all open files after any error.  This is helpful on Windows,
         * where holding deleted files open causes various strange errors.
         * It's not clear we need it elsewhere, but shouldn't hurt.
         */

        /* Since not using PG_TRY, must reset error stack by hand */
        t_thrd.log_cxt.error_context_stack = NULL;

        t_thrd.log_cxt.call_stack = NULL;

        /* Prevent interrupts while cleaning up */
        HOLD_INTERRUPTS();

        /* Report the error to the server log */
        EmitErrorReport();

        /* abort async io, must before LWlock release */
        AbortAsyncListIO();

#ifdef ENABLE_MOT
        /* cleanups any leftovers in other storage engines (release MOT snapshot lock if taken) */
        CallCheckpointCallback(EVENT_CHECKPOINT_ABORT, 0);
#endif

        /* release resource held by lsc */
        AtEOXact_SysDBCache(false);
        /*
         * These operations are really just a minimal subset of
         * AbortTransaction().	We don't have very many resources to worry
         * about in checkpointer, but we do have LWLocks, buffers, and temp
         * files.
         */
        LWLockReleaseAll();
        pgstat_report_waitevent(WAIT_EVENT_END);
        AbortBufferIO();
        UnlockBuffers();
        /* buffer pins are released here: */
        ResourceOwnerRelease(t_thrd.utils_cxt.CurrentResourceOwner, RESOURCE_RELEASE_BEFORE_LOCKS, false, true);
        /* we needn't bother with the other ResourceOwnerRelease phases */
        AtEOXact_Buffers(false);
        AtEOXact_SMgr();
        AtEOXact_Files();
        AtEOXact_HashTables(false);

        /* release compression ctx */
        crps_destory_ctxs();

        /* Warn any waiting backends that the checkpoint failed. */
        if (t_thrd.checkpoint_cxt.ckpt_active) {
            /* use volatile pointer to prevent code rearrangement */
            volatile CheckpointerShmemStruct* cps = t_thrd.checkpoint_cxt.CheckpointerShmem;

            SpinLockAcquire(&cps->ckpt_lck);
            cps->ckpt_failed++;
            cps->ckpt_done = cps->ckpt_started;
            SpinLockRelease(&cps->ckpt_lck);

            t_thrd.checkpoint_cxt.ckpt_active = false;
        }

        /*
         * Now return to normal top-level context and clear ErrorContext for
         * next time.
         */
        MemoryContextSwitchTo(checkpointer_context);
        FlushErrorState();

        /* Flush any leaked data in the top-level context */
        MemoryContextResetAndDeleteChildren(checkpointer_context);

        /* Now we can allow interrupts again */
        RESUME_INTERRUPTS();

        /*
         * Sleep at least 1 second after any error.  A write error is likely
         * to be repeated, and we don't want to be filling the error logs as
         * fast as we can.
         */
        pg_usleep(1000000L);
    }
    oldTryCounter = gstrace_tryblock_entry(&curTryCounter);

    /* We can now handle ereport(ERROR) */
    t_thrd.log_cxt.PG_exception_stack = &local_sigjmp_buf;

    /*
     * Unblock signals (they were blocked when the postmaster forked us)
     */
    gs_signal_setmask(&t_thrd.libpq_cxt.UnBlockSig, NULL);
    (void)gs_signal_unblock_sigusr2();

    /*
     * Use the recovery target timeline ID during recovery
     */
    if (RecoveryInProgress())
        t_thrd.xlog_cxt.ThisTimeLineID = GetRecoveryTargetTLI();

    /*
     * Ensure all shared memory values are set correctly for the config. Doing
     * this here ensures no race conditions from other concurrent updaters.
     */
    UpdateSharedMemoryConfig();

    /*
     * Advertise our latch that backends can use to wake us up while we're
     * sleeping.
     */
    g_instance.proc_base->checkpointerLatch = &t_thrd.proc->procLatch;

    /* init compression ctx for page compression */
    crps_create_ctxs(CHECKPOINT_THREAD);

    pgstat_report_appname("CheckPointer");
    pgstat_report_activity(STATE_IDLE, NULL);

    /*
     * Loop forever
     */
    for (;;) {
        bool do_checkpoint = false;
        bool do_dirty_flush = false;
        int flags = 0;
        pg_time_t now;
        int elapsed_secs;
        int cur_timeout;
        int rc;

        /* Clear any already-pending wakeups */
        ResetLatch(&t_thrd.proc->procLatch);

        pgstat_report_activity(STATE_RUNNING, NULL);

        /*
         * Process any requests or signals received recently.
         */
        CkptAbsorbFsyncRequests();

        if (t_thrd.checkpoint_cxt.got_SIGHUP) {
            t_thrd.checkpoint_cxt.got_SIGHUP = false;
            ProcessConfigFile(PGC_SIGHUP);
            u_sess->attr.attr_storage.CheckPointTimeout = ENABLE_INCRE_CKPT
                                                              ? u_sess->attr.attr_storage.incrCheckPointTimeout
                                                              : u_sess->attr.attr_storage.fullCheckPointTimeout;
            most_available_sync = (volatile bool) u_sess->attr.attr_storage.guc_most_available_sync;
            /*
             * Checkpointer is the last process to shut down, so we ask it to
             * hold the keys for a range of other tasks required most of which
             * have nothing to do with checkpointing at all.
             *
             * For various reasons, some config values can change dynamically
             * so the primary copy of them is held in shared memory to make
             * sure all backends see the same value.  We make Checkpointer
             * responsible for updating the shared memory copy if the
             * parameter setting changes because of SIGHUP.
             */
            UpdateSharedMemoryConfig();
        }

        if (bgwriter_first_startup && !RecoveryInProgress()) {
            t_thrd.checkpoint_cxt.checkpoint_requested = true;
            flags = CHECKPOINT_IMMEDIATE;
            bgwriter_first_startup = false;
            ereport(LOG, (errmsg("database first startup and recovery finish, so do checkpointer.")));
        }

        if (t_thrd.checkpoint_cxt.checkpoint_requested) {
            t_thrd.checkpoint_cxt.checkpoint_requested = false;
            do_checkpoint = true;
            u_sess->stat_cxt.BgWriterStats->m_requested_checkpoints++;
        }

        if (t_thrd.checkpoint_cxt.shutdown_requested || pmState == PM_SHUTDOWN) {
            /*
             * From here on, elog(ERROR) should end with exit(1), not send
             * control back to the sigsetjmp block above
             */
            u_sess->attr.attr_common.ExitOnAnyError = true;
            
            /* Close down the database */
            ShutdownXLOG(0, 0);

            /* release compression ctx */
            crps_destory_ctxs();

            /* Normal exit from the checkpointer is here */
            proc_exit(0); /* done */
        }

        /*
         * Force a checkpoint if too much time has elapsed since the last one.
         * Note that we count a timed checkpoint in stats only when this
         * occurs without an external request, but we set the CAUSE_TIME flag
         * bit even if there is also an external request.
         */
        now = (pg_time_t)time(NULL);
        elapsed_secs = now - t_thrd.checkpoint_cxt.last_checkpoint_time;

        if (elapsed_secs >= u_sess->attr.attr_storage.CheckPointTimeout) {
            if (!do_checkpoint)
                u_sess->stat_cxt.BgWriterStats->m_timed_checkpoints++;

            do_checkpoint = true;
            flags |= CHECKPOINT_CAUSE_TIME;
        }

        /*
         * Do a checkpoint if requested.
         */
        if (do_checkpoint) {
            bool ckpt_performed = false;
            bool do_restartpoint = false;

            /* use volatile pointer to prevent code rearrangement */
            volatile CheckpointerShmemStruct* cps = t_thrd.checkpoint_cxt.CheckpointerShmem;

            /*
             * Check if we should perform a checkpoint or a restartpoint. As a
             * side-effect, RecoveryInProgress() initializes TimeLineID if
             * it's not set yet.
             */
            do_restartpoint = RecoveryInProgress();

            /*
             * Atomically fetch the request flags to figure out what kind of a
             * checkpoint we should perform, and increase the started-counter
             * to acknowledge that we've started a new checkpoint.
             */
            SpinLockAcquire(&cps->ckpt_lck);
            flags |= cps->ckpt_flags;
            cps->ckpt_flags = 0;
            cps->ckpt_started++;
            SpinLockRelease(&cps->ckpt_lck);

            /*
             * The end-of-recovery checkpoint is a real checkpoint that's
             * performed while we're still in recovery.
             */
            if (flags & CHECKPOINT_END_OF_RECOVERY) {
                do_restartpoint = false;
            }

            /*
             * We will warn if (a) too soon since last checkpoint (whatever
             * caused it) and (b) somebody set the CHECKPOINT_CAUSE_XLOG flag
             * since the last checkpoint start.  Note in particular that this
             * implementation will not generate warnings caused by
             * CheckPointTimeout < CheckPointWarning.
             */
            if (!do_restartpoint && (flags & CHECKPOINT_CAUSE_XLOG) &&
                elapsed_secs < u_sess->attr.attr_storage.CheckPointWarning)
                ereport(LOG,
                    (errmsg_plural("checkpoints are occurring too frequently (%d second apart)",
                         "checkpoints are occurring too frequently (%d seconds apart)",
                         elapsed_secs,
                         elapsed_secs),
                        errhint("Consider increasing the configuration parameter \"checkpoint_segments\".")));

            /*
             * Initialize checkpointer-private variables used during
             * checkpoint
             */
            t_thrd.checkpoint_cxt.ckpt_active = true;

            if (!do_restartpoint)
                t_thrd.checkpoint_cxt.ckpt_start_recptr = GetInsertRecPtr();

            t_thrd.checkpoint_cxt.ckpt_start_time = now;
            t_thrd.checkpoint_cxt.ckpt_cached_elapsed = 0;

            if (flags & CHECKPOINT_FLUSH_DIRTY) {
                do_dirty_flush = true;
            }
            /*
             * Do a normal checkpoint/restartpoint.
             */
            if (do_dirty_flush) {
                ereport(LOG, (errmsg("[file repair] request checkpoint, flush all dirty page.")));
                Assert(RecoveryInProgress());
                if (ENABLE_INCRE_CKPT) {
                    g_instance.ckpt_cxt_ctl->full_ckpt_expected_flush_loc = get_dirty_page_queue_tail();
                    pg_memory_barrier();
                    if (get_dirty_page_num() > 0) {
                        g_instance.ckpt_cxt_ctl->flush_all_dirty_page = true;
                        ereport(LOG, (errmsg("[file repair] need flush %ld pages.", get_dirty_page_num())));
                        CheckPointBuffers(flags, true);
                    }
                } else {
                    CheckPointBuffers(flags, true);
                }
            } else if (!do_restartpoint && !SS_DISASTER_STANDBY_CLUSTER) {
                CreateCheckPoint(flags);
                ckpt_performed = true;
                if (!bgwriter_first_startup && CheckFpwBeforeFirstCkpt()) {
                    DisableFpwBeforeFirstCkpt();
                }
            } else {
                ckpt_performed = CreateRestartPoint(flags);
            }

            /*
             * After any checkpoint, close all smgr files.	This is so we
             * won't hang onto smgr references to deleted files indefinitely.
             */
            smgrcloseall();

            /*
             * Indicate checkpoint completion to any waiting backends.
             */
            SpinLockAcquire(&cps->ckpt_lck);
            cps->ckpt_done = cps->ckpt_started;
            SpinLockRelease(&cps->ckpt_lck);

            if (ckpt_performed) {
                /*
                 * Note we record the checkpoint start time not end time as
                 * t_thrd.checkpoint_cxt.last_checkpoint_time.  This is so that time-driven
                 * checkpoints happen at a predictable spacing.
                 */
                t_thrd.checkpoint_cxt.last_checkpoint_time = now;
            } else if (!do_dirty_flush) {
                /*
                 * We were not able to perform the restartpoint (checkpoints
                 * throw an ERROR in case of error).  Most likely because we
                 * have not received any new checkpoint WAL records since the
                 * last restartpoint. Try again in 15 s.
                 */
                t_thrd.checkpoint_cxt.last_checkpoint_time = now - u_sess->attr.attr_storage.CheckPointTimeout + 15;
            }

            t_thrd.checkpoint_cxt.ckpt_active = false;
        }

        /* Check for archive_timeout and switch xlog files if necessary. */
        CheckArchiveTimeout();

        /*
         * Send off activity statistics to the stats collector.  (The reason
         * why we re-use bgwriter-related code for this is that the bgwriter
         * and checkpointer used to be just one process.  It's probably not
         * worth the trouble to split the stats support into two independent
         * stats message types.)
         */
        pgstat_send_bgwriter();

        /*
         * Sleep until we are signaled or it's time for another checkpoint or
         * xlog file switch.
         */
        now = (pg_time_t)time(NULL);
        elapsed_secs = now - t_thrd.checkpoint_cxt.last_checkpoint_time;
        elapsed_secs = (elapsed_secs < 0) ? 0 : elapsed_secs;
        if (elapsed_secs >= u_sess->attr.attr_storage.CheckPointTimeout)
            continue; /* no sleep for us ... */

        cur_timeout = u_sess->attr.attr_storage.CheckPointTimeout - elapsed_secs;

        if (u_sess->attr.attr_common.XLogArchiveTimeout > 0 && !RecoveryInProgress()) {
            elapsed_secs = now - t_thrd.checkpoint_cxt.last_xlog_switch_time;

            if (elapsed_secs >= u_sess->attr.attr_common.XLogArchiveTimeout)
                continue; /* no sleep for us ... */

            cur_timeout = Min(cur_timeout, u_sess->attr.attr_common.XLogArchiveTimeout - elapsed_secs);
        }

        pgstat_report_activity(STATE_IDLE, NULL);
        rc = WaitLatch(&t_thrd.proc->procLatch,
            WL_LATCH_SET | WL_TIMEOUT | WL_POSTMASTER_DEATH,
            cur_timeout * 1000L /* convert to ms */);

        /*
         * Emergency bailout if postmaster has died.  This is to avoid the
         * necessity for manual cleanup of all postmaster children.
         */
        if (rc & WL_POSTMASTER_DEATH) {

            /* release compression ctx */
            crps_destory_ctxs();

            gs_thread_exit(1);
        }
    }
}

/*
 * CheckArchiveTimeout -- check for archive_timeout and switch xlog files
 *
 * This will switch to a new WAL file and force an archive file write
 * if any activity is recorded in the current WAL file, including just
 * a single checkpoint record.
 */
static void CheckArchiveTimeout(void)
{
    pg_time_t now;
    pg_time_t last_time;

    if (u_sess->attr.attr_common.XLogArchiveTimeout <= 0 || RecoveryInProgress())
        return;

    now = (pg_time_t)time(NULL);

    /* First we do a quick check using possibly-stale local state. */
    if ((int)(now - t_thrd.checkpoint_cxt.last_xlog_switch_time) < u_sess->attr.attr_common.XLogArchiveTimeout)
        return;

    /*
     * Update local state ... note that t_thrd.checkpoint_cxt.last_xlog_switch_time is the last time
     * a switch was performed *or requested*.
     */
    last_time = GetLastSegSwitchTime();

    t_thrd.checkpoint_cxt.last_xlog_switch_time = Max(t_thrd.checkpoint_cxt.last_xlog_switch_time, last_time);

    /* Now we can do the real check */
    if ((int)(now - t_thrd.checkpoint_cxt.last_xlog_switch_time) >= u_sess->attr.attr_common.XLogArchiveTimeout) {
        XLogRecPtr switchpoint;

        /* OK, it's time to switch */
        switchpoint = RequestXLogSwitch();

        /*
         * If the returned pointer points exactly to a segment boundary,
         * assume nothing happened.
         */
        if ((switchpoint % XLogSegSize) != 0)
            ereport(DEBUG1,
                (errmsg("transaction log switch forced (archive_timeout=%d)",
                    u_sess->attr.attr_common.XLogArchiveTimeout)));

        /*
         * Update state in any case, so we don't retry constantly when the
         * system is idle.
         */
        t_thrd.checkpoint_cxt.last_xlog_switch_time = now;
    }
}

/*
 * Returns true if an immediate checkpoint request is pending.	(Note that
 * this does not check the *current* checkpoint's IMMEDIATE flag, but whether
 * there is one pending behind it.)
 */
static bool ImmediateCheckpointRequested(void)
{
    if (t_thrd.checkpoint_cxt.checkpoint_requested) {
        volatile CheckpointerShmemStruct* cps = t_thrd.checkpoint_cxt.CheckpointerShmem;

        /*
         * We don't need to acquire the ckpt_lck in this case because we're
         * only looking at a single flag bit.
         */
        if (cps->ckpt_flags & CHECKPOINT_IMMEDIATE)
            return true;
    }

    return false;
}

/*
 * CheckpointWriteDelay -- control rate of checkpoint
 *
 * This function is called after each page write performed by BufferSync().
 * It is responsible for throttling BufferSync()'s write rate to hit
 * checkpoint_completion_target.
 *
 * The checkpoint request flags should be passed in; currently the only one
 * examined is CHECKPOINT_IMMEDIATE, which disables delays between writes.
 *
 * 'progress' is an estimate of how much of the work has been done, as a
 * fraction between 0.0 meaning none, and 1.0 meaning all done.
 */
void CheckpointWriteDelay(int flags, double progress)
{
    /* Do nothing if checkpoint is being executed by non-checkpointer process */
    if (!AmCheckpointerProcess())
        return;

    /*
     * Perform the usual duties and take a nap, unless we're behind schedule,
     * in which case we just try to catch up as quickly as possible.
     */
    if (!((uint32)flags & CHECKPOINT_IMMEDIATE) && !t_thrd.checkpoint_cxt.shutdown_requested &&
        !ImmediateCheckpointRequested() && IsCheckpointOnSchedule(progress)) {
        if (t_thrd.checkpoint_cxt.got_SIGHUP) {
            t_thrd.checkpoint_cxt.got_SIGHUP = false;
            ProcessConfigFile(PGC_SIGHUP);
            most_available_sync = (volatile bool)u_sess->attr.attr_storage.guc_most_available_sync;
            /* update shmem copies of config variables */
            UpdateSharedMemoryConfig();
        }

        CkptAbsorbFsyncRequests();
        t_thrd.checkpoint_cxt.absorbCounter = WRITES_PER_ABSORB;

        CheckArchiveTimeout();

        /*
         * Report interim activity statistics to the stats collector.
         */
        pgstat_send_bgwriter();

        /*
         * This sleep used to be connected to bgwriter_delay, typically 200ms.
         * That resulted in more frequent wakeups if not much work to do.
         * Checkpointer and bgwriter are no longer related so take the Big
         * Sleep.
         */
        pg_usleep(100000L);
    } else if (--t_thrd.checkpoint_cxt.absorbCounter <= 0) {
        /*
         * Absorb pending fsync requests after each WRITES_PER_ABSORB write
         * operations even when we don't sleep, to prevent overflow of the
         * fsync request queue.
         */
        CkptAbsorbFsyncRequests();
        t_thrd.checkpoint_cxt.absorbCounter = WRITES_PER_ABSORB;
    }
}

/*
 * IsCheckpointOnSchedule -- are we on schedule to finish this checkpoint
 *		 in time?
 *
 * Compares the current progress against the time/segments elapsed since last
 * checkpoint, and returns true if the progress we've made this far is greater
 * than the elapsed time/segments.
 */
static bool IsCheckpointOnSchedule(double progress)
{
    XLogRecPtr recptr;
    struct timeval now;
    double elapsed_xlogs, elapsed_time;

    Assert(t_thrd.checkpoint_cxt.ckpt_active);
    u_sess->attr.attr_storage.CheckPointTimeout = ENABLE_INCRE_CKPT
                                                      ? u_sess->attr.attr_storage.incrCheckPointTimeout
                                                      : u_sess->attr.attr_storage.fullCheckPointTimeout;

    /* Scale progress according to checkpoint_completion_target. */
    progress *= u_sess->attr.attr_storage.CheckPointCompletionTarget;

    /*
     * Check against the cached value first. Only do the more expensive
     * calculations once we reach the target previously calculated. Since
     * neither time or WAL insert pointer moves backwards, a freshly
     * calculated value can only be greater than or equal to the cached value.
     */
    if (progress < t_thrd.checkpoint_cxt.ckpt_cached_elapsed)
        return false;

    /*
     * Check progress against WAL segments written and checkpoint_segments.
     *
     * We compare the current WAL insert location against the location
     * computed before calling CreateCheckPoint. The code in XLogInsert that
     * actually triggers a checkpoint when checkpoint_segments is exceeded
     * compares against RedoRecptr, so this is not completely accurate.
     * However, it's good enough for our purposes, we're only calculating an
     * estimate anyway.
     */
    if (!RecoveryInProgress()) {
        recptr = GetInsertRecPtr();
        elapsed_xlogs = (((double)(recptr - t_thrd.checkpoint_cxt.ckpt_start_recptr)) / XLogSegSize) /
                        (u_sess->attr.attr_storage.CheckPointSegments);

        if (progress < elapsed_xlogs) {
            t_thrd.checkpoint_cxt.ckpt_cached_elapsed = elapsed_xlogs;
            return false;
        }
    }

    /*
     * Check progress against time elapsed and checkpoint_timeout.
     */
    gettimeofday(&now, NULL);
    elapsed_time = ((double)((pg_time_t)now.tv_sec - t_thrd.checkpoint_cxt.ckpt_start_time) + now.tv_usec / 1000000.0) /
                   u_sess->attr.attr_storage.CheckPointTimeout;

    if (progress < elapsed_time) {
        t_thrd.checkpoint_cxt.ckpt_cached_elapsed = elapsed_time;
        return false;
    }

    /* It looks like we're on schedule. */
    return true;
}

/* --------------------------------
 *		signal handler routines
 * --------------------------------
 */
/*
 * chkpt_quickdie() occurs when signalled SIGQUIT by the postmaster.
 *
 * Some backend has bought the farm,
 * so we need to stop what we're doing and exit.
 */
static void chkpt_quickdie(SIGNAL_ARGS)
{
    gs_signal_setmask(&t_thrd.libpq_cxt.BlockSig, NULL);

    /*
     * We DO NOT want to run proc_exit() callbacks -- we're here because
     * shared memory may be corrupted, so we don't want to try to clean up our
     * transaction.  Just nail the windows shut and get out of town.  Now that
     * there's an atexit callback to prevent third-party code from breaking
     * things by calling exit() directly, we have to reset the callbacks
     * explicitly to make this work as intended.
     */
    on_exit_reset();

    /*
     * Note we do exit(2) not exit(0).	This is to force the postmaster into a
     * system reset cycle if some idiot DBA sends a manual SIGQUIT to a random
     * backend.  This is necessary precisely because we don't clean up our
     * shared memory state.  (The "dead man switch" mechanism in pmsignal.c
     * should ensure the postmaster sees this as a crash, too, but no harm in
     * being doubly sure.)
     */

    /* release compression ctx */
    crps_destory_ctxs();

    exit(2);
}

/* SIGHUP: set flag to re-read config file at next convenient time */
static void ChkptSigHupHandler(SIGNAL_ARGS)
{
    int save_errno = errno;

    t_thrd.checkpoint_cxt.got_SIGHUP = true;

    if (t_thrd.proc)
        SetLatch(&t_thrd.proc->procLatch);

    errno = save_errno;
}

/* SIGINT: set flag to run a normal checkpoint right away */
static void ReqCheckpointHandler(SIGNAL_ARGS)
{
    int save_errno = errno;

    t_thrd.checkpoint_cxt.checkpoint_requested = true;

    if (t_thrd.proc)
        SetLatch(&t_thrd.proc->procLatch);

    errno = save_errno;
}

/* SIGUSR1: used for latch wakeups */
static void chkpt_sigusr1_handler(SIGNAL_ARGS)
{
    int save_errno = errno;

    latch_sigusr1_handler();

    errno = save_errno;
}

/* SIGUSR2: set flag to run a shutdown checkpoint and exit */
static void ReqShutdownHandler(SIGNAL_ARGS)
{
    int save_errno = errno;

    t_thrd.checkpoint_cxt.shutdown_requested = true;

    if (t_thrd.proc)
        SetLatch(&t_thrd.proc->procLatch);

    errno = save_errno;
}

/* --------------------------------
 *		communication with backends
 * --------------------------------
 */
/*
 * CheckpointerShmemSize
 *		Compute space needed for checkpointer-related shared memory
 */
const uint DDL_REQUEST_MAX = 100000;
Size CheckpointerShmemSize(void)
{
    Size size;

    /*
     * Currently, the size of the requests[] array is arbitrarily set equal to
     * NBuffers.  This may prove too large or small ...
     */
    size = offsetof(CheckpointerShmemStruct, requests);
    if (ENABLE_INCRE_CKPT) {
        /* incremental checkpoint, the checkpoint thread only handle the drop table request and drop db request */
        size = add_size(size, mul_size(DDL_REQUEST_MAX, sizeof(CheckpointerRequest)));
    } else {
        size = add_size(size, mul_size(TOTAL_BUFFER_NUM, sizeof(CheckpointerRequest)));
    }

    return size;
}

/*
 * CheckpointerShmemInit
 *		Allocate and initialize checkpointer-related shared memory
 */
void CheckpointerShmemInit(void)
{
    Size size = CheckpointerShmemSize();
    bool found = false;

    t_thrd.checkpoint_cxt.CheckpointerShmem =
        (CheckpointerShmemStruct*)ShmemInitStruct("Checkpointer Data", size, &found);

    if (!found) {
        /*
         * First time through, so initialize.  Note that we zero the whole
         * requests array; this is so that CompactCheckpointerRequestQueue
         * can assume that any pad bytes in the request structs are zeroes.
         */
        /* The memory of the memset sometimes exceeds 2 GB. so, memset_s cannot be used. */
        MemSet((char*)t_thrd.checkpoint_cxt.CheckpointerShmem, 0, size);
        SpinLockInit(&t_thrd.checkpoint_cxt.CheckpointerShmem->ckpt_lck);
        t_thrd.checkpoint_cxt.CheckpointerShmem->max_requests = ENABLE_INCRE_CKPT ? DDL_REQUEST_MAX : TOTAL_BUFFER_NUM;
    }
}

/*
 * Check wheter checkpoint proc is running while waiting request checkpoint to finish.
 */
static void CheckPointProcRunning(void)
{
    if (g_instance.pid_cxt.CheckpointerPID == 0) {
        ereport(FATAL,
            (errcode(ERRCODE_WITH_CHECK_OPTION_VIOLATION),
                errmsg("could not request checkpoint because checkpointer not running")));
    }
}

/*
 * RequestCheckpoint
 *		Called in backend processes to request a checkpoint
 *
 * flags is a bitwise OR of the following:
 *	CHECKPOINT_IS_SHUTDOWN: checkpoint is for database shutdown.
 *	CHECKPOINT_END_OF_RECOVERY: checkpoint is for end of WAL recovery.
 *	CHECKPOINT_IMMEDIATE: finish the checkpoint ASAP,
 *		ignoring checkpoint_completion_target parameter.
 *	CHECKPOINT_FORCE: force a checkpoint even if no XLOG activity has occurred
 *		since the last one (implied by CHECKPOINT_IS_SHUTDOWN or
 *		CHECKPOINT_END_OF_RECOVERY).
 *	CHECKPOINT_WAIT: wait for completion before returning (otherwise,
 *		just signal checkpointer to do it, and return).
 *	CHECKPOINT_CAUSE_XLOG: checkpoint is requested due to xlog filling.
 *		(This affects logging, and in particular enables CheckPointWarning.)
 */
void RequestCheckpoint(int flags)
{
    /* use volatile pointer to prevent code rearrangement */
    volatile CheckpointerShmemStruct* cps = t_thrd.checkpoint_cxt.CheckpointerShmem;
    int ntries;
    int old_failed, old_started;
    /*
     * If in a standalone backend, just do it ourselves.
     */
    if (!IsPostmasterEnvironment) {
        /*
         * There's no point in doing slow checkpoints in a standalone backend,
         * because there's no other backends the checkpoint could disrupt.
         */
        CreateCheckPoint(flags | CHECKPOINT_IMMEDIATE);

        /*
         * After any checkpoint, close all smgr files.	This is so we won't
         * hang onto smgr references to deleted files indefinitely.
         */
        smgrcloseall();

        return;
    }

    /*
     * Atomically set the request flags, and take a snapshot of the counters.
     * When we see ckpt_started > old_started, we know the flags we set here
     * have been seen by checkpointer.
     *
     * Note that we OR the flags with any existing flags, to avoid overriding
     * a "stronger" request by another backend.  The flag senses must be
     * chosen to make this work!
     */
    SpinLockAcquire(&cps->ckpt_lck);
    old_failed = cps->ckpt_failed;
    old_started = cps->ckpt_started;
    cps->ckpt_flags |= flags;
    SpinLockRelease(&cps->ckpt_lck);

    /*
     * Send signal to request checkpoint.  It's possible that the checkpointer
     * hasn't started yet, or is in process of restarting, so we will retry a
     * few times if needed.  Also, if not told to wait for the checkpoint to
     * occur, we consider failure to send the signal to be nonfatal and merely
     * LOG it.
     */
    for (ntries = 0;; ntries++) {
        if (t_thrd.checkpoint_cxt.CheckpointerShmem->checkpointer_pid == 0) {
            /* max wait CheckPointWaitTime secs */
            if (ntries >= (u_sess->attr.attr_storage.CheckPointWaitTimeOut * 10) || pmState == PM_SHUTDOWN_2) {
                if (flags & CHECKPOINT_WAIT) {
                    ereport(ERROR,
                        (errcode(ERRCODE_WITH_CHECK_OPTION_VIOLATION),
                            errmsg("could not request checkpoint because checkpointer not running")));
                } else {
                    ereport(LOG, (errmsg("could not request checkpoint because checkpointer not running")));
                }   
                break;
            }
        } else if (gs_signal_send(t_thrd.checkpoint_cxt.CheckpointerShmem->checkpointer_pid, SIGINT) != 0) {
            /* max wait CheckPointWaitTime secs */
            if (ntries >= (u_sess->attr.attr_storage.CheckPointWaitTimeOut * 10)) { 
                if (flags & CHECKPOINT_WAIT) {
                    ereport(ERROR,
                        (errcode(ERRCODE_WITH_CHECK_OPTION_VIOLATION), errmsg("could not signal for checkpoint: %m")));
                } else {
                    ereport(LOG, (errmsg("could not signal for checkpoint: %m")));
                } 
                break;
            }
        } else {
            break; /* signal sent successfully */
        }

        CHECK_FOR_INTERRUPTS();
        pg_usleep(100000L); /* wait 0.1 sec, then retry */
    }

    /*
     * If requested, wait for completion.  We detect completion according to
     * the algorithm given above.
     */
    if (flags & CHECKPOINT_WAIT) {
        int new_started, new_failed;

        /* Wait for a new checkpoint to start. */
        for (;;) {
            SpinLockAcquire(&cps->ckpt_lck);
            new_started = cps->ckpt_started;
            SpinLockRelease(&cps->ckpt_lck);

            if (new_started != old_started) {
                break;
            }

            CHECK_FOR_INTERRUPTS();
            CheckPointProcRunning();
            pg_usleep(100000L);
        }

        /*
         * We are waiting for ckpt_done >= new_started, in a modulo sense.
         */
        for (;;) {
            int new_done;

            SpinLockAcquire(&cps->ckpt_lck);
            new_done = cps->ckpt_done;
            new_failed = cps->ckpt_failed;
            SpinLockRelease(&cps->ckpt_lck);

            if (new_done - new_started >= 0) {
                break;
            }

            CHECK_FOR_INTERRUPTS();
            CheckPointProcRunning();
            pg_usleep(100000L);
        }

        if (new_failed != old_failed)
            ereport(ERROR,
                (errcode(ERRCODE_WITH_CHECK_OPTION_VIOLATION),
                    errmsg("checkpoint request failed"),
                    errhint("Consult recent messages in the server log for details.")));
    }
}

/*
 * ForwardSyncRequest
 *      Forward a file-fsync request from a backend to the checkpointer
 *
 * Whenever a backend is compelled to write directly to a relation
 * (which should be seldom, if the background writer is getting its job done),
 * the backend calls this routine to pass over knowledge that the relation
 * is dirty and must be fsync'd before next checkpoint.  We also use this
 * opportunity to count such writes for statistical purposes.
 *
 * To avoid holding the lock for longer than necessary, we normally write
 * to the requests[] queue without checking for duplicates.  The checkpointer
 * will have to eliminate dups internally anyway.  However, if we discover
 * that the queue is full, we make a pass over the entire queue to compact
 * it.  This is somewhat expensive, but the alternative is for the backend
 * to perform its own fsync, which is far more expensive in practice.  It
 * is theoretically possible a backend fsync might still be necessary, if
 * the queue is full and contains no duplicate entries.  In that case, we
 * let the backend know by returning false.
 */
bool CkptForwardSyncRequest(const FileTag *ftag, SyncRequestType type)
{
    CheckpointerRequest* request = NULL;
    bool too_full = false;

    if (!IsUnderPostmaster) {
        return false;           /* probably shouldn't even get here */
    }

    if (AmCheckpointerProcess()) {
        ereport(ERROR,
            (errcode(ERRCODE_WITH_CHECK_OPTION_VIOLATION),
                errmsg("ForwardFsyncRequest must not be called in checkpointer")));
    }

    LWLockAcquire(CheckpointerCommLock, LW_EXCLUSIVE);

    /* Count all backend writes regardless of if they fit in the queue */
    if (!AmBackgroundWriterProcess() && !AmPageWriterProcess()) {
        t_thrd.checkpoint_cxt.CheckpointerShmem->num_backend_writes++;
    }

    /*
     * If the checkpointer isn't running or the request queue is full, the
     * backend will have to perform its own fsync request.	But before forcing
     * that to happen, we can try to compact the request queue.
     */
    if (t_thrd.checkpoint_cxt.CheckpointerShmem->checkpointer_pid == 0 ||
        (t_thrd.checkpoint_cxt.CheckpointerShmem->num_requests >=
        t_thrd.checkpoint_cxt.CheckpointerShmem->max_requests &&
        !CompactCheckpointerRequestQueue())) {
        /*
         * Count the subset of writes where backends have to do their own
         * fsync
         */
        if (!AmBackgroundWriterProcess() && !AmPageWriterProcess()) {
            t_thrd.checkpoint_cxt.CheckpointerShmem->num_backend_fsync++;
        }

        LWLockRelease(CheckpointerCommLock);
        return false;
    }

    /* OK, insert request */
    request =
        &t_thrd.checkpoint_cxt.CheckpointerShmem->requests[t_thrd.checkpoint_cxt.CheckpointerShmem->num_requests++];
    request->ftag = *ftag;
    request->type = type;

    /* If queue is more than half full, nudge the checkpointer to empty it */
    too_full = (t_thrd.checkpoint_cxt.CheckpointerShmem->num_requests >=
                t_thrd.checkpoint_cxt.CheckpointerShmem->max_requests / 2);

    LWLockRelease(CheckpointerCommLock);

    /* ... but not till after we release the lock */
    if (too_full && g_instance.proc_base->checkpointerLatch) {
        SetLatch(g_instance.proc_base->checkpointerLatch);
    }

    return true;
}

int getDuplicateRequest(CheckpointerRequest *requests, int num_requests, bool *skip_slot)
{
    struct CheckpointerSlotMapping {
        CheckpointerRequest request;
        int slot;
    };

    int n;
    int num_skipped = 0;
    HASHCTL ctl;
    HTAB* htab = NULL;

    /* Initialize temporary hash table */
    errno_t rc = memset_s(&ctl, sizeof(ctl), 0, sizeof(ctl));
    securec_check(rc, "\0", "\0");
    ctl.keysize = sizeof(CheckpointerRequest);
    ctl.entrysize = sizeof(struct CheckpointerSlotMapping);
    ctl.hash = CheckpointerRequestHash;
    ctl.match = CheckpointerRequestMatch;
    ctl.hcxt = CurrentMemoryContext;

    htab = hash_create("CompactRequestQueue", num_requests, &ctl,
        HASH_ELEM | HASH_FUNCTION | HASH_CONTEXT | HASH_COMPARE);

    /*
     * The basic idea here is that a request can be skipped if it's followed
     * by a later, identical request.  It might seem more sensible to work
     * backwards from the end of the queue and check whether a request is
     * *preceded* by an earlier, identical request, in the hopes of doing less
     * copying.  But that might change the semantics, if there's an
     * intervening FORGET_RELATION_FSYNC or FORGET_DATABASE_FSYNC request, so
     * we do it this way.  It would be possible to be even smarter if we made
     * the code below understand the specific semantics of such requests (it
     * could blow away preceding entries that would end up being canceled
     * anyhow), but it's not clear that the extra complexity would buy us
     * anything.
     */

    for (n = 0; n < num_requests; n++) {
        CheckpointerRequest* request = NULL;
        struct CheckpointerSlotMapping* slotmap;
        bool found = false;

        /*
         * We use the request struct directly as a hashtable key.  This
         * assumes that any padding bytes in the structs are consistently the
         * same, which should be okay because we zeroed them in
         * CheckpointerShmemInit.  Note also that RelFileNode had better
         * contain no pad bytes.
         */
        request = &requests[n];
        slotmap = (CheckpointerSlotMapping*)hash_search(htab, request, HASH_ENTER, &found);

        if (found) {
            /* Duplicate, so mark the previous occurrence as skippable */
            skip_slot[slotmap->slot] = true;
            num_skipped++;
        }

        /* Remember slot containing latest occurrence of this request value */
        slotmap->slot = n;
    }

    /* Done with the hash table. */
    hash_destroy(htab);

    /* If no duplicates, we're out of luck. */
    if (!num_skipped) {
        return 0;
    }

    return num_skipped;
}

/*
 * CompactCheckpointerRequestQueue
 *		Remove duplicates from the request queue to avoid backend fsyncs.
 *		Returns "true" if any entries were removed.
 *
 * Although a full fsync request queue is not common, it can lead to severe
 * performance problems when it does happen.  So far, this situation has
 * only been observed to occur when the system is under heavy write load,
 * and especially during the "sync" phase of a checkpoint.	Without this
 * logic, each backend begins doing an fsync for every block written, which
 * gets very expensive and can slow down the whole system.
 *
 * Trying to do this every time the queue is full could lose if there
 * aren't any removable entries.  But that should be vanishingly rare in
 * practice: there's one queue entry per shared buffer.
 */
static bool CompactCheckpointerRequestQueue(void)
{
    int preserve_count;
    bool* skip_slot = NULL;
    int num_skipped = 0;

    /* must hold CheckpointerCommLock in exclusive mode */
    Assert(LWLockHeldByMe(CheckpointerCommLock));

    /* Initialize skip_slot array */
    skip_slot = (bool*)palloc0(sizeof(bool) * t_thrd.checkpoint_cxt.CheckpointerShmem->num_requests);

    num_skipped = getDuplicateRequest(t_thrd.checkpoint_cxt.CheckpointerShmem->requests,
        t_thrd.checkpoint_cxt.CheckpointerShmem->num_requests, skip_slot);

    /* If no duplicates, we're out of luck. */
    if (num_skipped == 0) {
        pfree(skip_slot);
        return false;
    }

    /* We found some duplicates; remove them. */
    preserve_count = 0;

    for (int n = 0; n < t_thrd.checkpoint_cxt.CheckpointerShmem->num_requests; n++) {
        if (skip_slot[n])
            continue;

        t_thrd.checkpoint_cxt.CheckpointerShmem->requests[preserve_count++] =
            t_thrd.checkpoint_cxt.CheckpointerShmem->requests[n];
    }

    ereport(DEBUG1,
        (errmsg("compacted fsync request queue from %d entries to %d entries",
            t_thrd.checkpoint_cxt.CheckpointerShmem->num_requests,
            preserve_count)));
    t_thrd.checkpoint_cxt.CheckpointerShmem->num_requests = preserve_count;

    /* Cleanup. */
    pfree(skip_slot);
    return true;
}

/*
 * AbsorbFsyncRequests
 *		Retrieve queued fsync requests and pass them to local smgr.
 *
 * This is exported because it must be called during CreateCheckPoint;
 * we have to be sure we have accepted all pending requests just before
 * we start fsync'ing.  Since CreateCheckPoint sometimes runs in
 * non-checkpointer processes, do nothing if not checkpointer.
 */
void CkptAbsorbFsyncRequests(void)
{
    CheckpointerRequest* requests = NULL;
    CheckpointerRequest* request = NULL;
    int n;

    if (!AmCheckpointerProcess())
        return;

    /*
     * We have to PANIC if we fail to absorb all the pending requests (eg,
     * because our hashtable runs out of memory).  This is because the system
     * cannot run safely if we are unable to fsync what we have been told to
     * fsync.  Fortunately, the hashtable is so small that the problem is
     * quite unlikely to arise in practice.
     */
    START_CRIT_SECTION();

    /*
     * We try to avoid holding the lock for a long time by copying the request
     * array.
     */
    LWLockAcquire(CheckpointerCommLock, LW_EXCLUSIVE);

    /* Transfer stats counts into pending pgstats message */
    u_sess->stat_cxt.BgWriterStats->m_buf_written_backend +=
        t_thrd.checkpoint_cxt.CheckpointerShmem->num_backend_writes;
    u_sess->stat_cxt.BgWriterStats->m_buf_fsync_backend += t_thrd.checkpoint_cxt.CheckpointerShmem->num_backend_fsync;

    t_thrd.checkpoint_cxt.CheckpointerShmem->num_backend_writes = 0;
    t_thrd.checkpoint_cxt.CheckpointerShmem->num_backend_fsync = 0;

    n = t_thrd.checkpoint_cxt.CheckpointerShmem->num_requests;

    if (n > 0) {
        errno_t rc;
        requests = (CheckpointerRequest*)palloc(n * sizeof(CheckpointerRequest));
        rc = memcpy_s(requests,
            n * sizeof(CheckpointerRequest),
            t_thrd.checkpoint_cxt.CheckpointerShmem->requests,
            n * sizeof(CheckpointerRequest));
        securec_check(rc, "\0", "\0");
    }

    t_thrd.checkpoint_cxt.CheckpointerShmem->num_requests = 0;

    LWLockRelease(CheckpointerCommLock);

    for (request = requests; n > 0; request++, n--) {
        RememberSyncRequest(&request->ftag, request->type);
    }
    if (requests != NULL) {
        pfree(requests);
    }
    END_CRIT_SECTION();
}

/*
 * Update any shared memory configurations based on config parameters
 */
static void UpdateSharedMemoryConfig(void)
{
    /* update global shmem state for sync rep */
    SyncRepUpdateSyncStandbysDefined();

    /*
     * If full_page_writes has been changed by SIGHUP, we update it in shared
     * memory and write an XLOG_FPW_CHANGE record.
     */
    UpdateFullPageWrites();

    ereport(DEBUG2, (errmsg("checkpointer updated shared memory configuration values")));
}

/*
 * FirstCallSinceLastCheckpoint allows a process to take an action once
 * per checkpoint cycle by asynchronously checking for checkpoint completion.
 */
bool FirstCallSinceLastCheckpoint(void)
{
    /* use volatile pointer to prevent code rearrangement */
    volatile CheckpointerShmemStruct* cps = t_thrd.checkpoint_cxt.CheckpointerShmem;
    int new_done;
    bool FirstCall = false;

    SpinLockAcquire(&cps->ckpt_lck);
    new_done = cps->ckpt_done;
    SpinLockRelease(&cps->ckpt_lck);

    if (new_done != t_thrd.checkpoint_cxt.ckpt_done)
        FirstCall = true;

    t_thrd.checkpoint_cxt.ckpt_done = new_done;

    return FirstCall;
}

bool CheckpointInProgress(void)
{
    bool inProgress = false;
    volatile CheckpointerShmemStruct* cps = t_thrd.checkpoint_cxt.CheckpointerShmem;
    SpinLockAcquire(&cps->ckpt_lck);
    if (cps->ckpt_done != cps->ckpt_started) {
        inProgress = true;
    }
    SpinLockRelease(&cps->ckpt_lck);
    ereport(LOG, (errmsg("CheckpointInProgress: ckpt_done=%d, ckpt_started=%d",
        cps->ckpt_done, cps->ckpt_started)));
    return inProgress;
}

#ifdef ENABLE_MOT
void RegisterCheckpointCallback(CheckpointCallback callback, void* arg)
{
    CheckpointCallbackItem *item;

    item = (CheckpointCallbackItem*)MemoryContextAlloc(
        INSTANCE_GET_MEM_CXT_GROUP(MEMORY_CONTEXT_STORAGE), sizeof(CheckpointCallbackItem));
    item->callback = callback;
    item->arg = arg;
    item->next = g_instance.ckpt_cxt_ctl->ckptCallback;
    g_instance.ckpt_cxt_ctl->ckptCallback = item;
}

void CallCheckpointCallback(CheckpointEvent checkpointEvent, XLogRecPtr lsn)
{
    CheckpointCallbackItem* item;

    for (item = g_instance.ckpt_cxt_ctl->ckptCallback; item; item = item->next) {
        (*item->callback) (checkpointEvent, lsn, item->arg);
    }
}
#endif
